How Riots Start, and How They Can Be Stopped: Edward Glaeser

Aug. 12 (Bloomberg) -- The riots that began in London have
spread across the country. Decades of social-science research
has delivered insights about these outbursts of violence, but
hasn’t explained why they erupt when and where they do.

We do, however, understand how they usually end: with
overwhelmingly force that clears the streets.

Riots are more common in democracies, and the U.S. has had
its fair share. The deadliest was the 1863 Draft Riot. More than
120 people were killed when the streets of Manhattan were taken
over by protesters, many of them immigrants, who were furious at
the prospect of having to fight in the Civil War.

In the early decades of the 20th century, cities such as
Atlanta and Chicago were torn apart as whites attacked newly
urban blacks for perceived transgressions. Chicago’s 1919 riot
began when a child crossed an invisible racial barrier while
swimming in Lake Michigan. In the 1960s, there was widespread
unrest. In many cases, including the 1965 Watts Riot, the
violence began with an argument over law enforcement.

These public disturbances are a classic example of tipping-point phenomena, which occur when there is some positive
feedback mechanism that makes an activity more attractive, or
less costly, as more people do it.

Tipping Point

There is a tipping point in rioting because the cost of
participating -- the risk of going to jail -- gets lower as the
number of people involved increases. If I decided to start
rioting tomorrow in Harvard Square to express my outrage at the
closing of the beloved Curious George children’s bookstore, it’s
a pretty good bet that I would be immediately arrested. But if
thousands of others were involved, I’d probably get off scot
free. The police would be overwhelmed, and my probability of
incarceration would fall to zero.

Thus, riots occur when the shear mass of rioters overwhelms
law enforcement. But how do these mass events get started?

In some cases, such as the New York Draft Riot, organizers
get people out on the street. In others, such as the 1965 Watts
Riot, a peaceful crowd provides cover for initial lawlessness.
Sporting events, such as Game 7 of the Stanley Cup Finals in
Vancouver this year, can easily produce the crowds that allow a
riot to start. Most strangely, riots can follow an event that
creates a combination of anger and the shared perception that
others will be rioting. The acquittal of police officers in the
Rodney King case seems to have created these conditions in Los
Angeles in 1992.

London Shooting

The London riots appear to have had a simpler starting
point. About 300 people gathered at a police station to protest
the shooting of a 29-year-old suspect. Once there were so many
angry people in one place, setting fire to an empty police car
became a low-risk piece of pyrotechnics for the protesters.

After riots, there is often an attempt to explain the
outburst as the result of large societal forces. The events in
the U.K. have been blamed on growing inequality and the current
government’s austerity program. The disorder in the U.S. in the
1960s was attributed to racism.

But across U.S. cities, there has never been much of a link
between unrest and either inequality or poverty. In fact, the
riots of the 1960s were actually slightly more common in cities
that had more government spending. Riots were significantly
less common in the South, where the Jim Crow laws were making
their long overdue exit. This isn’t to say that many people
involved in riots don’t have valid grievances, but plenty of
people have serious grievances and don’t riot.

Police Presence

Somewhat paradoxically, even though the police often
provide the flash point for these outbreaks, larger police
expenditures per capita in a city in 1960 was associated with
fewer arrests and arsons when riots occurred. Even if a riot
provides a wakeup call for police reform, in the short run, the
outbreaks typically end only when there is enough law
enforcement to ensure that such behavior leads to arrests.

I hope the U.K. can handle its violence with a purely
police response, but in the U.S. restoring law has typically
meant bringing in the military. The 1863 Draft Riot ended when
federal troops arrived after a long march from Maryland.
Detroit’s terrible 1967 tumult ended with tanks on the streets.
The National Guard was deployed in Los Angeles in 1992. Trying
to stop a riot with too small a force can often lead to more,
not less, bloodshed, because as the riot continues, vigilantes
step in and beleaguered policemen can resort to brutality.

Mass Arrests

My colleague Christopher Stone has argued that there is
another lesson about fighting riots to be learned from the
incidents in the Paris suburbs in 2005, and the violence that
didn’t happen during the Republican National Convention in New
York City in 2004. In France, the police initially arrested
relatively few people, but sought serious criminal penalties for
those they did arrest. The New York Police Department arrested
more than 1,000 people and let them go. The New York strategy
protected the city; the French strategy wasn’t as effective.

The lesson: Light penalties widely applied and serious
penalties applied to a few can both deter unlawful behavior.
This is a central conclusion of Gary Becker’s path-breaking
economic analysis of crime and punishment. But in the case of
riots, it is awfully hard to actually prove wrongdoing and
extremely important to clear the streets. Arresting widely and
temporarily can be far more effective.

Riots strike at the very soul of cities. Even when they are
connected to understandable grievances, they do great harm,
particularly to the poorest residents. We all want the unrest in
the U.K. to end with a minimum of bloodshed and brutality. The
best way to achieve that end is with sufficient numbers of
police on the streets and gentle but restraining incarceration.

(Edward Glaeser, an economics professor at Harvard
University, is a Bloomberg View columnist. He is the author of
“Triumph of the City.” The opinions expressed are his own.)